The present invention relates to the field of cobalt base superalloys.
Service conditions in gas turbine engines are constantly increasing in severity and improved turbine materials are required for satisfactory operation. Cobalt base alloys are often used in turbine engines particularly in areas where high operating temperatures are encountered. Conventional base cobalt alloys almost invariably contain tantalum and columbium which to date, have been believed to provide improved elevated temperature properties.
U.S. Pat. No. 3,432,294 discloses an alloy having a composition similar to the alloy of the invention except that the alloy of the reference contains from 2-5% tantalum and contains lower levels of titanium and zirconium than the present alloy. There is no suggestion in this reference that the elimination of tantalum would have any beneficial effects. Canadian Pat. No. 639,056 also discloses an alloy similar to the present invention but the alloy of this reference contains from 1-4% tantalum or columbium. Additionally, other elements of the alloy of this reference are present in different amounts than the alloy of the present invention. Likewise, U.S. Pat. No. 3,677,939, assigned to the assignee of the present invention, has a composition similar to the composition of the present invention except for the presence of columbium and tantalum.
The present invention discloses an alloy substantially free from both columbium and tantalum which also has superior mechanical properties to alloys which contain columbian and tantalum.
This body of art and, in fact, the experience of those skilled in the art, clearly demonstrates that the cobalt superalloy is one in which small but critical limitations are often determinative as to whether or not a given alloy is usable for the purpose intended. Nor is the art one of reasonable empirical certainty as the results of small changes in either the character or proportions of an alloy are not normally truly predictable.